A is father of C and D is son of B. E is brother of A. If C is sister of D, how is B related to E ?

Answer: A. Daughter
A is father of C and C is sister of D.
So, A is father of D. But D is son of B.
So, B is the mother of D and wife of A. Also, E is the brother of A.
So, B is the sister-in-law of E.